A battery and a power supply device which are installed in an electric car and so forth are insulated from a car body and other circuits to prevent an electric shock. For such insulation for the battery and the power supply device, in the past, a leak detection device that detects leakage (a leak) caused by insufficient insulation has been proposed. In PTL 1, a technique of detecting the presence or absence of a leak by varying a portion of a resistance value of insulation resistance between a battery using an assembled battery and a ground and detecting the insulation resistance at this time has been disclosed.